A potential disaster was narrowly avoided when "at least" one commuter train came within seconds of smashing into tonnes of rubble blocking tracks near a major station, a union has warned.
Debris was left strewn across four lines outside Liverpool's main Lime Street station when a wall collapsed in deep cuttings at rush-hour on Tuesday.
Hundreds of passengers were trapped on trains stuck in tunnels outside the hub which handles more than 15 million passenger journeys each year.
Tens of thousands of passengers have faced days of disruption since the incident that cut the station off from the network, with services only beginning to resume on Thursday.
The Rail, Maritime and Transport (RMT) union said it understands "at least one train was seconds away from colliding with the collapse and that the damage caused to the four lines affected is so severe that they could be out of action for a month".
The union said it was thanks to the actions of train guards that travellers were evacuated safely - and warned of the "potentially lethal consequences" had the trains been driver-only.
RMT general secretary Mick Cash said the response by railway staff and emergency services was "magnificent" and it was "very lucky indeed that this was not a major disaster".
"Without guards to keep passengers calm and lead safe evacuations, we would have had the potentially lethal prospect of passengers de-training themselves in cold, dark tunnels and stumbling towards tons of debris and damaged 25,000-volt overhead power lines."
Mr Cash said the incident was "yet another graphic illustration" that the driver-only trains planned by Arrival Rail North (Northern) would be a "fundamental attack on safety for passengers and rail workers alike".
All services between Lime Street and Manchester, Warrington and Wigan were significantly impacted by the collapse.
The operator said the services that are able to run are expected to be "extremely busy".
It is not known when all the lines will be back in full working order.
The trackside wall collapsed around 5.45pm on Tuesday night between Lime Street and Edge Hill station.
Network Rail said five large containers, each holding many tonnes of material, had been stacked by a third party on elevated land beside the collapsed section of wall.
Three trains had to be evacuated but there were no reports of any injuries.
Mark Killick, chief operating officer for Network Rail, said trains were expected to be running in and out of the station again by Thursday March 9.
He said: "After the wall collapsed on Tuesday night, our orange army engineers have devised a three-step plan.
"Firstly, we are making the location safe. That is happening now.
"This will allow us to start step two - safely accessing the tracks in the cutting more than 10 metres below to clear the debris.
"We will then move on to step three - repairing the damaged railway."